Systems and methods for constructing and testing composite photonic structures

ABSTRACT

Systems and methods are disclosed relating to composite photonic materials used to design structures and detecting material deformation for the purpose of monitoring structural health of physical structures. According to one aspect, a composite structure is provided that includes a base material, an optical diffraction grating and one or more fluorophore materials constructed such that localized perturbations create a measurable change in the structure&#39;s diffraction pattern. An inspection device is also provided that is configured to detect perturbations in the composite structure. The inspection device is configured to emit an inspecting radiation into the structure and capture the refracted radiation and measure the change in the diffraction pattern and quantify the perturbation based on the wavelength and the angular information for the diffracted radiation.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a divisional application of U.S. patentapplication Ser. No. 15/082,327 filed on Mar. 28, 2016, entitled SYSTEMSAND METHODS FOR CONSTRUCTING AND TESTING COMPOSITE PHOTONIC STRUCTURES,the contents of which is hereby incorporated by reference as if setforth in its entirety herein.

FIELD OF THE INVENTION

The present invention relates to composite photonic structures andnon-destructive inspection systems and methods, in particular to systemsand methodologies for constructing composite photonic structures andinspection systems and methods for detecting perturbations in thestructures for the purpose of structural health monitoring.

BACKGROUND

The availability of non-destructive inspection techniques for structuralmaterials, for instance, nonmetallic pipes used in pipelines, islimited. For the most part, the techniques available so far are eitherdestructive to the material or are experimental and unreliable. Evenconsidering current experimental techniques for non-destructiveinspection, no current techniques are able to reliably predict theformation of defects, and are generally used to detect only existingdefects.

More specifically, existing building materials and the correspondingsystems and techniques for inspection of the materials are inadequatefor detecting the presence of stresses on or in the material such astensile stress or compressive stress with sufficient accuracy andprecision such that defects can be predicted before they occur.

Currently available technologies for sensing material defects aregenerally based on mono-dimensional fiber Bragg gratings. These fibersprovide mono-dimensional information: i.e., they can detect only stressthat occurs along the length of the fiber, and only substantial stressesthat correspond to already damaged materials with significant cracks andruptures in the structural material.

There is a need for systems and methods for detecting perturbations instructural materials that utilize a photonic material, such as anoptical grating or a photonic crystal, as a sensitive element fordiffraction generation. In addition, there is a need for systems andmethods for detecting perturbations in structural materials thatquantify deformations in photonic materials through a wavelength change,or a diffraction angle change quantified from an intensity variation.Moreover, there is a need for systems and methods for detectingperturbations with a sensitivity that is tunable through the choice ofthe inspecting wavelength and the corresponding periodicity of thephotonic structural material. In addition, there is a need for systemsand methods for detecting perturbations that have a multi-dimensionallevel of sensitivity.

It is with respect to these and other considerations that the disclosuremade herein is presented.

SUMMARY

According to an aspect of the present invention, there is provided acomposite photonic structure which comprises one or more layers of anon-metallic structural material, a diffractive refractive grating inregistry with at least one layer of structural material, and one or morefluorophore materials disposed within the composite structure. Thegrating includes a plurality of features that are arranged to haveperiodicity in at least one dimension.

According to a further aspect, the grating can comprise a discrete layerof one or more grating materials disposed over an entire surface of atleast one layer of the structural material, a surface of at least onelayer of the structural material, or a combination of theseconstructions. The grating in this or other embodiments can extend overa top surface, a bottom surface, or both surfaces of at least one of thelayers of structural material. In still further aspects, the gratinglayer can separate two layers of the structural material, and the pluralfeatures of the grating can be arranged to have periodicity in at leasttwo dimensions.

In further aspects, alone or in combination with the foregoing, thefluorophore can comprise a fluorophore that is excited by radiationhaving a first wavelength and which emits radiation having a secondwavelength upon excitation, wherein the one or more layers of structuralmaterial and the grating are transparent to radiation having the firstand second wavelengths. In certain embodiments, the fluorophore can beincorporated into the composite structure as a separate layer ofmaterial that includes at least the fluorophore material, as a dopant ornano-material that is embedded in a region within at least one of theone or more layers of structural material, or a combination of theforegoing.

In still further aspects, a device for non-destructive inspection of aphotonic structure having a periodic refraction grating is providedwhich comprises a lamp configured to emit a cone of radiation toward andonto a portion of a sample, the radiation having constant intensity overa range of wavelengths. A camera sensor is configured to capture animage of diffracted radiation, wherein the diffracted radiation is theradiation emitted by the lamp as diffracted by the portion of thesample, and wherein the image provides one or more wavelengths of theradiation captured at each respective point on the captured image. Acomputer readable storage medium including one or more software modulesincluding an analysis module is included, wherein each module includesexecutable code. A processor is communicatively coupled to the lamp, thecamera sensor and the storage medium, wherein the processor isconfigured by executing the code in the one or more software modules toanalyze the image of the captured radiation in order to determine adisplacement of any perturbations within the portion of the sample by,for each point on the captured image: transforming the wavelength at thepoint to a first periodicity value for a corresponding point within theportion of the sample as a function of a position of the lamp and thecamera sensor relative to the sample and a diffraction angle for thecorresponding point within the portion of the sample, and computing anamount of deformation for the corresponding point based on the firstperiodicity value and a reference periodicity. A visual display is insignal communication with the processor, wherein the processor isconfigured to output an image of the sample representing the amount ofdeformation computed for each corresponding point within the portion ofthe sample using the display.

An inspection device according to still further aspects can furthercomprise a laser emitter configured to emit a beam of radiation having aspecific wavelength onto a particular location on the sample and adetector configured to capture at least one diffracted beam and measurean intensity of the at least one captured beam and a correspondingposition on the detector, wherein the at least one diffracted beam is aresult of the sample diffracting the emitted beam. In such an inspectiondevice, the processor is further configured by executing the one or moresoftware modules to receive the measured intensity and the correspondingposition for the at least one captured beam and determine a displacementof any perturbations at the particular location on the sample by:calculating a diffraction angle for the particular location on thesample as a function of the corresponding position of the at least onecaptured beam, and calculating a second periodicity value for theparticular location on the sample according to the calculateddiffraction angle and a prescribed grating characteristic of the sample,and computing an amount of deformation for the particular location basedon a difference between the second periodicity value and a referenceperiodicity for the particular location.

These and other aspects, features, and advantages can be appreciatedfrom the accompanying description of certain embodiments of theinvention and the accompanying drawing figures and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a high-level diagram illustrating an exemplary compositestructure with a fluorescent layer and a two dimensional grating withone dimensional periodicity according to an embodiment of the invention;

FIG. 2 is a high-level diagram illustrating an exemplary compositestructure with a fluorescent layer and a two dimensional grating withone dimensional periodicity according to an embodiment of the invention;

FIG. 3 is a high-level diagram illustrating an exemplary compositestructure with a fluorescent layer and a two dimensional grating withtwo dimensional periodicity according to an embodiment of the invention;

FIG. 4 is a high-level diagram illustrating an exemplary compositestructure with two fluorescent layers and a two dimensional grating withtwo dimensional periodicity according to an embodiment of the invention;

FIG. 5A is a high-level diagram illustrating an exemplary compositestructure with structured parallel strips of fluorescent material and atwo dimensional grating with one dimensional periodicity according to anembodiment of the invention;

FIG. 5B depicts a top view of an exemplary diffraction pattern caused bythe embodiment of FIG. 5A;

FIG. 6A is a high-level diagram illustrating an exemplary compositestructure with two perpendicular sets of structured strips offluorescent material and a two dimensional grating with two dimensionalperiodicity according to an embodiment of the invention;

FIG. 6B depicts a top view of an exemplary diffraction pattern caused bythe embodiment of FIG. 6A;

FIG. 7 is a high-level diagram illustrating an exemplary tube-shapedcomposite structure with structured parallel and perpendicular strips offluorescent material and a two dimensional grating with two dimensionalperiodicity according to an embodiment of the invention;

FIG. 8A is a high-level diagram illustrating an exemplary compositestructure including rods defining a three dimensional photonic crystalas a grating according to an embodiment of the invention;

FIG. 8B is a high-level diagram illustrating an exemplary compositestructure including rods defining a three dimensional photonic crystalas a grating according to an embodiment of the invention;

FIG. 9 is a high-level diagram illustrating an exemplary compositestructure including beads defining a three dimensional photonic crystalas a grating according to an embodiment of the invention;

FIG. 10 is a high-level diagram illustrating an exemplary compositestructure including voids defining a three dimensional grating and a oneor more fluorophore materials according to an embodiment of theinvention;

FIG. 11A is a high-level diagram illustrating an exemplary configurationof a monochromator utilizing a stretchable grating as a diffractionelement;

FIG. 11B is a high-level diagram illustrating the exemplaryconfiguration of the monochromator of FIG. 11A utilizing a stretchablediffraction grating in stretch conditions as a wavelength selectionmechanism.

FIG. 12A is a high-level diagram illustrating a top view of an exemplaryinspection device according to an embodiment of the invention;

FIG. 12B is a high-level diagram illustrating a front perspective viewof the exemplary inspection device of FIG. 12A according to anembodiment of the invention;

FIG. 12C is a block diagram illustrating exemplary configuration ofcomputer hardware and software components of the inspection device ofFIG. 12A according to an embodiment of the invention;

FIG. 13A is a flow diagram illustrating a routine for computingdeformation of a photonic structure according to an embodiment of theinvention;

FIG. 13B is a flow diagram illustrating a routine for computingdeformation of a photonic structure according to an embodiment of theinvention;

FIG. 14A is a high-level diagram illustrating a front perspective viewof an exemplary inspection device according to an embodiment of theinvention;

FIG. 14B is a high-level diagram illustrating a rear perspective view ofthe exemplary inspection device of FIG. 14A according to an embodimentof the invention;

FIG. 15A is a high-level diagram illustrating a top view of an exemplaryinspection device according to an embodiment of the invention;

FIG. 15B is a high-level diagram illustrating a front perspective viewof the exemplary inspection device of FIG. 15A according to anembodiment of the invention;

FIG. 16A is a screenshot of an exemplary wavelength map as captured byan exemplary inspection device according to an embodiment of theinvention;

FIG. 16B is a screenshot of an exemplary wavelength map as captured byan exemplary inspection device according to an embodiment of theinvention;

FIG. 17 is a high level diagram illustrating a side perspective view ofan exemplary inspection device comprising radiation sources withadjustable positions over at least 2 degrees of motion according to anembodiment of the invention; and

FIG. 18 is a high level diagram illustrating a bottom-side view of anexemplary inspection device with positionable radiation sourcesaccording to an embodiment of the invention.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS OF THE INVENTION

By way of overview and introduction, systems and methodologies fordetecting material deformation primarily for the purpose of structuralhealth monitoring are disclosed herein. According to a first aspect, acomposite material/structure that can be used to construct engineeredstructures is disclosed. The composite includes a base material (e.g., astructural material such as a non-metallic plate or pipe), an opticaldiffraction grating and one or more fluorophore materials. In someimplementations, the composite structure does not include a fluorescentmaterial. In some implementations, the grating can be a surface of thebase material or a separate layer of material (e.g., a thin layer ofaluminum). The materials of the composite structure are arranged suchthat deformation of one or more of the materials of the compositestructure, e.g., perturbations caused by, for example and withoutlimitation, tensile stress, compressive stress, bending, temperaturevariations, and chemical composition changes and other material defects,locally changes the periodicity of the grating, or the refractive indexof one or both materials, for instance, by changing the size of thefeatures and/or the relative distance between the features of thegrating. This creates a measurable change in the diffraction patterncaused by composite structure that is proportional to the size of theperturbation and, using an inspection device, can be quantified as awavelength shift for a specific angle of diffraction according to theexpected diffraction characteristics of the grating as defined by agratings equation.

The fluorophore or fluorophores can be inserted into the base materialas dopants, nano-materials, or provided as a discrete material layerthat is separate from the base material. In addition or alternatively,one or more layers of fluorophore material can be embedded in thegrating material or a surrounding layer of material.

According to another aspect, devices and methods for non-destructiveinspection of the exemplary composite structures are also disclosedherein. The inspection device is configured to detect perturbations inthe composite structure based on diffraction of an inspecting radiationand the radiation generated by fluorophores within the compositestructure. More specifically, the inspection device is configured toemit an inspecting radiation onto or into the composite structure andcapture the diffracted radiation as an input and measure the change inthe diffraction pattern from an expected pattern. It can be appreciatedthat changes in one or more boundary behaviors of the radiation wavescan occur and be captured and measured. Changes in behavior includediffraction, reflection and refraction of the radiation and one or moreof the foregoing behaviors, and combinations thereof, can be measured,for instance, the inspecting radiation can be reflected and diffracted,or refracted, reflected and diffracted, or refracted and diffracted etc.Accordingly, it can be appreciated that the common phenomenon is thediffraction of the radiation.

The inspection device provides as an output, a quantification of theperturbation affecting the composite structure. In particular, theinspection device transforms the wavelength and/or the angle informationinto a measure of displacement. The inspection device consists of one ortwo components together utilizing two similar principles to achieve sucha transformation. One component transforms the wavelength informationinto a displacement, while the other component transforms the angularinformation into a displacement. Each component can work independentlyfrom the other. The periodic structure considered could be for example adiffraction grating such as the one depicted in FIG. 1 and describedherein.

The Composite Structure

As noted above, in accordance with one or more of the disclosedembodiments, the composite structure includes a base material (e.g., astructural material such as a metallic or, preferably, a non-metallicplate or pipe), an optical diffraction grating, or photonic crystal, andcan also include a one or more fluorophore materials (e.g., . . . ). Insome implementations, the grating can be a surface of the base materialor a separate layer of material (e.g., a thin layer of aluminum, or anyother reflective metal or material, etc.).

The grating does not have to be necessarily a material on its own, butcan be defined by any interface with periodic features between materialswith different refractive indices, one of which can also be air, or anyother gas, or liquid. More in general the diffractive role played by thediffraction grating represented in FIGS. 1 to 7 can be performed by aphotonic crystal. Such a photonic crystal can be defined as a periodicmodulation of refractive index within a certain region of space that isable to generate a photonic band structure similar to the way in which acrystalline solid or semiconductor generates an electronic energy levelstructure, or electronic band structure (with conduction and valencebands). As an extension, any crystalline material can be also consideredas a photonic crystal with a periodicity size in the order of Å that isable to generate a photonic band structure in the x-ray region of thespectrum, which is measurable by X-ray diffraction. In most cases theposition of the photonic band gap, or the entire photonic band structurecan be calculated according to literature using a combination of theBragg's law for diffraction and Snell's law for refraction. In themajority of applications for human scale and interests, the size of theperiodicity of the structure to detect defects can be tuned around thesubmicron to micron scale, which will generate response in theUV-visible to NIR range of the electromagnetic spectrum. However,applications beyond this range both at smaller and higher scales arealso possible. The dimensionality of the system can range from 1D to nD.The practical periodicities are 1, 2, and 3 Dimensional. In 1 Dimensionthe photonic crystal can be represented as a Fiber Bragg Grating, aPhotonic Crystal Fiber Bragg Grating, or anything whose periodicityvaries along one direction. In 2 Dimension the photonic crystal can be adiffraction grating, or a monolayer of particles distributedperiodically on a surface, or a periodic distribution of holes arrangedin 2 Dimensions, as depicted in FIGS. 1 to 7, or also in this case aPhotonic Crystal Fiber Bragg Grating. In 3 Dimensions the photoniccrystal can be an Opal, or any periodic distribution of features thatgenerate a modulation of the refractive index.

The one or more fluorophores to be inserted inside the photonicstructure can be any active material with an emission wavelength able tointeract with the photonic band structure generated by the periodicphotonic structure and ultimately determined by the size of theperiodicity, which in turn is determined by the degree of sensitivityrequired. The emission profile of the fluorophore can be very narrow orbroad depending on the interaction mechanism with the photonicstructure. For example, if the displacement is measured as intensityrelated to a change in the diffraction angle, a narrow emission profileof the fluorophore will result in a more sudden intensity change as aconsequence of a displacement in the material. However, above a certainvalue of displacement, the intensity will be lost (because it will bedeviated away from the photodetector, and thus the system won't besensitive to even larger displacements. If the emission profile of thefluorophore is broad, the intensity change won't be as sudden, but itwill be measurable for a larger range of displacement. On an even moresensitive scenario, a fluorophore could present multiple emission peaks,so that the change in intensity is sharp for small displacements, whileit remain sensitive even for larger displacements, as another emissionpeak will collide with the detector. The same result can be obtained byinserting different fluorophores into the same structure. For thesereasons, the fluorophores can be organic molecules with broad andintense emission bands, or transition metal ions, or Lanthanide ionswith sharp emission peaks, or Quantum Dots, or semiconductornanocrystals with emission bands determined by quantum confinement andthus tunable both in energy and to a certain extent in broadness.

The size of the periodic features of the grating are comparable in sizeto the size of the perturbation to be detected, in one embodiment.Furthermore, it such an embodiment the material constituting the gratingcan have a flexibility which is sufficient to respond to a perturbationwithin itself or within its surroundings.

Such a composite structure can be configured to work both in reflectionand in transmission mode. The materials that define the composite, inone implementation, is of the type that allows the inspecting radiationto pass therethrough. In this or other implementations, the grating canbe shaped out of one material attached or placed in proximity to anothermaterial, or it can be fabricated as the interface between two materialswith different refractive indices.

In one exemplary configuration, the fluorophore has a narrow emissionband so as to improve detection of the fluorophore when excited. Inaddition, the fluorophore can be placed on the opposite side of the basematerial with respect to the inspection device. Accordingly, the basematerial, grating and fluorophore are selected to allow transmission ofthe inspecting radiation and radiation emitted by the fluorophore. Thisexemplary composite structure configuration can enhance sensitivity andsimplify the detection of perturbations in the material. The reason isthat the aforementioned wavelength shift for a quasi-monochromaticradiation will result in the presence or absence of radiation as aresult of a small perturbation. Such a change is easier to detectbecause: it provides a higher sensitivity contrast; can be detected as asimple change in intensity rather than wavelength shift, thussimplifying the detection system and reducing its cost; it eliminatesthe need of a broad band excitation source; and the excitation sourceand detection system can be placed on the same side with respect to thegrating, and can be incorporated into a single device, without losingangular resolution or sensitivity contrast.

These and other exemplary configurations in which one or more layers ofbase material, fluorophore and the grating surface are layered arefurther described more specifically herein. These configurations includevarious two and three dimensional arrangements of the one or morefluorophores within the composite, for instance, as parallel rods,perpendicular meshes and three dimensional lattices. According to afurther aspect, the composite can include one or more photonic crystalsand quantum dots to define the grating layer and, in someimplementations, the fluorescent layer as well.

In accordance with one or more of the disclosed embodiments, anexemplary configuration of the composite can include a regular twodimensional grating with periodicity along one direction and the one ormore fluorophores can be embedded in a material layer parallel to thesurface of the grating. A composite structure 100 having such aconfiguration is represented in FIG. 1.

From the embodiment of FIG. 1 it is possible to appreciate few of theadvantages of the invention. The grating 120 in this case is formedbetween material 110 and material 130. Material 110 and 130 presentdifferent refractive indices. Material 110 can also be air, whilematerial 130 could in principle be air but more commonly a solidmaterial. The grating surface 120 can be the simple interface betweenthe two materials or made by a thin layer of another material such asfor example Aluminum. The material 140 is not necessary for the purposeof the device, but it is defined in case the fabrication procedureincludes the fabrication of the grating as a standalone piece made ofmaterial 130. Material 150 contains one or more fluorophores. It can bethe same material as material 140, which in turn, as aforementioned, canbe the same material as material 130. The one or more fluorophores canbe inserted in material 150 as a dopant, a nano-material, or material150 can be fluorescent itself. Material 170 can be a protection layerfor the fluorescent layer, or it can be absent. The opticalcharacteristics of materials 110, 130, 140, 150, and 170, in certainimplementations, have at least partial transparency at the wavelength ofexcitation of the one or more fluorophores and also at its emissionwavelength.

In operation, as the radiation of excitation, represented as λ_(ex)(e.g., radiation emitted by an inspection device), reaches the gratingsurface 120, a diffraction pattern is generated both in reflection andtransmission mode. As would be understood by those in the art, a gratingresponds to a white light source by decomposing it into differentwavelengths, while a grating responds to a laser beam by diffracting itinto separate beams emerging from the grating at different anglesdepending on the diffraction order. As shown in FIG. 1, the inspectionradiation is a beam λ, emitted by a laser source of an inspection device(not shown). In the exemplary embodiment shown in FIG. 1, only thereflection mode is considered and the “m” values in the figure representthe orders of diffraction for respective diffracted beams. As shown, thediffracted beams (e.g., m=0, 1, 2) reach the fluorescent layer atdifferent positions determined by the structure of the grating. In thesepositions the fluorescent layer will emit radiation producing a 1 or 2dimensional image of such pattern that can be imaged/captured by aspecially configured inspection device, as further described below. Anyperturbation in the material such as defects, compressive and tensilestresses, bending, and twisting will affect the diffraction pattern andthus the image formed by the fluorescent layer. The spots 160A-160Eshown in FIG. 1 are the regions of the fluorescent layer through whichthe diffracted radiation is passing or absorbed and that are emittingradiation as a result of being exited by the diffracted radiation.

As a consequence of a perturbation in the so constructed compositestructure and, more specifically perturbation affecting the periodicityof the grating surface 20, the parameters that can change in thediffraction pattern are: the distance between each spot, the size andshape of each spot, and with it, the intensity distribution. As aresult, analysis of the reflection to detect such perturbations caninclude monitoring the intensity or radiation in a particular point,within one or more of: the emitting spot, at a specific distance orrelative to the excitation beam. In this way the detector can be mountedand fixed on the same device containing the excitation source. Thechanges in intensity measured at that specific point, not only indicatethe presence of a perturbation but also the extent of the perturbation,and the type of perturbation. For example, a tensile stress can push thespots 160A-160E apart from each other therefore it will result in adecrease in intensity of radiation on the left side of the spot 6A (onthe far right in FIG. 1), or an increase on that spot's right side. Asimilar response can be caused by a bending force that generates aconvex, or negative, curvature in the grating. The opposite response canoccur if the stress is compressive or if the bending is causing apositive curvature on the grating. In the case of twisting the spot willmove sideways and the intensity will change according to the sameprinciple.

FIG. 2 depicts another exemplary configuration of the composite inaccordance with one or more embodiments of the invention. In particular,as shown in FIG. 2, the fluorescent layer 250 is placed below thegrating surface 220. Material 210 can be the base support for the entirecomposite structure and material 250 is the material layer includingfluorescent material. In some implementations it can be a material thatcontains one or more fluorophores or it can be a fluorescent itself. Inaddition or alternatively, material 210 is not necessarily included, asmaterial 250 can perform the function of base material and the one ormore fluorophores can be contained within material 250. Material layer230 provides a separation between the fluorescent layer and the grating.Also this material is not strictly necessary, however, in practicalapplications material layer 230 can provide a useful separation andfurther support layer. Finally, the grating surface 220 is on top and,in some implementations, can be made of a separate material frommaterial 230 or it can be shaped out of material 230.

FIG. 3 depicts another exemplary configuration of a composite structure300 in accordance with one or more embodiments of the invention. Asshown in FIG. 3, the fluorescent layer 350 is placed below the grating380. Material 310 can be the base support for the entire compositestructure and material layer 330 can be the structural material. Asshown, material layer 350 is the layer including the fluorescentmaterial. Moreover, as shown in FIG. 3, the grating 380 utilized is twodimensional, such as, for example, a periodic distribution of holeswithin a slab of another material. As a result, this will generate a twodimensional diffraction pattern, which will allow for a more direct wayto detect anisotropy of perturbation in the grating or in the materialwith which the grating is in contact. The holes depicted in the figure(e.g., hole 385), can be actual holes or regions made of a materialhaving a different refractive index from the remaining material definingthe grating. In one or more implementations, the optical characteristicsof this top layer having holes or such regions include: a material thatis transparent for the excitation radiation, unless the radiation isdirected to pass through a gap in it; a material having a differentrefractive index with respect to the rest of the layer; and a materialthat is at least partially transparent for the wavelength of the emittedradiation.

In FIGS. 1, 2 and 3 it is indicated the different orders of diffractionm=1, . . . n, and “n” is truncated to two for easiness of depiction inthe figures, however, the useful diffraction order can reach higherorder depending on the structure of the grating, the distance betweenthe fluorescent layer and the grating, the distance between the gratingand the observer (e.g., inspection device), and in general thearchitecture of the device and the detection system. While the gratingdepicted in FIG. 1 presents a mono-dimensional periodicity and thegrating in FIG. 3 presets a two-dimensional periodicity, a gratinghaving any type of periodicity can be used for the two exemplarycomposite architectures, depending on the diffraction characteristicsdesired. The advantage of a grating with two-dimensional periodicity isthat it will generate a diffraction pattern with information about thetwo dimensional anisotropy of the stress. For example, in the case of atensile stress along a particular direction, the distance increasebetween the diffraction spots will be only along that particulardirection.

In another exemplary embodiment of the invention, as shown in FIG. 4, acomposite structure 400 can include two fluorescent layers. Theconstruction of the composite 400 shown in FIG. 4 is similar to theexemplary configuration shown in FIG. 2 that has a fluorescent layerbelow the grating surface but also includes a second fluorescent layer490 above the grating. More specifically, bottom layer 410 can serve asa support for the fluorescent layer 450 and, in some variations, is notnecessary if the material layer 450 that includes one or morefluorophores is configured to be a structural material layer includingone or more fluorophores therein. Layer 430 is a separation layerbetween the fluorescent layer 450 and the grating layer 480. Layer 480is the grating, which as shown, can be a separate material layer.However, in some implementations, separation layer 430 and 480 can becombined, except that the holes shown in grating layer 480 can comprisea material with a different refractive index. Layer 440 is a separationlayer between the grating and the second fluorescent layer and can beeither a structural material layer or, in some implementations, air.Finally layer 490 is an additional top fluorescent material layer.

The purpose of this added fluorescent layer 490 is to simplify thevisualization of the diffraction pattern and thus the detection ofperturbations in the composite structure system. In operation, aradiation λ_(ex) can be shone through the structure 400 onto a spot 460on the fluorescent layer 450. The excited fluorescent spot 460 emitslight in all direction and partially passes through layer 430 andcrosses the grating 480. At this point, due to the diffraction grating,the radiation is diffracted and proceeds through layer 440 toward layer490 as individual beams, shown as m=0 through m=2. Due to the additionalfluorescent layer 490, these beams are visualized as fluorescent spots465 shown by the top fluorescent layer 490. The purpose of this topfluorescent layer 495 is to facilitate the visualization of these beams.

The excitation radiation is selected such that its wavelength is notcompletely absorbed by the layers of material comprising the composite400 through which the radiation passes, except fluorophore layer 450.Minimal or no radiation absorption in the non-fluorescent layer(s) ispreferable in order to ensure that the fluorescent layer 450 receivesthe excitation radiation. The fluorescent material 450 is also selectedsuch that its wavelength of emission from layer 450 (the “first emissionradiation”) also passes undisturbed through layer 430, which ispreferably at least partially transparent for this wavelength ofradiation. The layer 480 could be made of two materials with differentrefractive indices, or the cylindrical holes can be simply empty. Bothmaterials are preferably transparent to the excitation radiation, while,with respect to the emission radiation, they can be either transparentor at least the material constituting the cylindrical holes in thefigure needs to be at least partially transparent.

In the case that the grating 480 is not a two dimensional photoniccrystal, as shown in FIG. 4, but instead is a grating surface like thegrating 120 depicted in FIG. 1, the requirement is that both material430 and 440 are be at least partially transparent for the first emissionradiation. With such an architecture, layer 480 need not be a discretelayer and can be a grating surface separating (e.g., defining theinterface between) layer 430 and 440. Layer 440, in any case should betransparent for the same radiation emitted by layer 450. Layer 480 canalso be a three dimensional photonic structure, in this case similarconsiderations as for the grating displayed in FIG. 4 are validregarding the transparency of the two constituent materials. Thefluorescent layer 490 can be selected such that it absorbs the emissionradiation from 450 and is excited by the emission radiation and, assuch, emits a second emission radiation with a different wavelength thanthe first emission radiation. Alternatively, the top layer 490, insteadof being a fluorescent layer, can be simply a screen on which the imageis visualized.

In some exemplary arrangements, a composite can be constructed such thatthe grating is above the one or more fluorophores and the one or morefluorophores are arranged within the material in such a way that they donot extend through the entire area of a surface of the material belowthe grating. An exemplary configuration of a composite structure 500having such a configuration in accordance with one or more embodimentsof the invention is shown in FIG. 5A.

As shown in FIG. 5A, the fluorescent portion of the material is anarrangement of parallel strips 530 embedded within the structuralmaterial 510 and below the grating surface 520, which defines the topsurface of the material layer 510. The inspection illumination in thiscase does not have to be a laser, but it can be a lamp emitting lightincluding an excitation wavelength that is chosen based on the one ormore fluorophores utilized (e.g., based on its particular excitationwavelength). In this way the strips of fluorescent material inside thematerial 530 will appear to light up upon excitation. FIG. 5B depicts atop view of the diffraction pattern that is formed by the set ofparallel fluorescent rods embedded periodically below the grating. Asshown, the radiation from each of the excited fluorescent rods show asrespective strips 511. In addition, the areas in between the fluorescentstripes (e.g., strips 512) will also present lines of emission as aresult of the diffraction of the fluorescent lines from the grating. Bymonitoring these lines and the pattern formed, it is possible to detectany deformation, as a deformation of the material would cause amovement, a change of shape, or a shift of these lines from the expectedpattern. For these reasons, from a detection point of view, it ispossible to monitor only one spot and detect the change of emissionintensity coming from that specific spot. Therefore, a deformation couldbe detected as an interruption of signal or as a start of signal.

Further to the foregoing example in which the fluorescent materials arearranged within the structural material according to a pattern havingperiodicity in one direction, different fluorescent patterns can be usedto create the composite structure depending on the anisotropy of theinformation desired. FIG. 6A, depicts an exemplary configuration of acomposite structure 600 formed of a structural material 610 having a topgrating surface 620 and embedded fluorescent material 630 therein. Asshown, the fluorescent material is arranged as two sets of parallellines (that each have a width and a thickness) that are perpendicular toone another and the grating surface is a two dimensional grating withtwo dimensional periodicity. FIG. 6B depicts a top view of the compositestructure and depicts the diffraction pattern that is formed by the twosets of parallel fluorescent lines that are oriented perpendicularly toone another. In particular, lines 611 correspond to the emittedradiation from the fluorescent lines oriented across the length of thestructure 600 and the lines 612 formed in the area in between thefluorescent stripes are lines of emission as a result of the diffractionof the fluorescent lines from the grating 620. A similar pattern ofradiation lines 614 are also emitted by the length-wise fluorescentstrips. In use, parallel lines of fluorescent material can be useful todetect perturbations perpendicular to them, as a perturbation along thesame direction would have little effect on them. Alternatively, agrating made of two sets of parallel lines perpendicular to each othercan provide information regarding perturbations affecting the materialin one or more of two directions of space.

Accordingly, a so constructed material, can be monitored and itsparticular construction used to detect the amount of perturbation,stress, or deformation to which the material is exposed. In particular,the exemplary construction makes it possible to quantify the extent ofdeformation. For example, if the material only includes a grating, anydeformation will result in a wavelength change. On the other hand, inthe presence of one or more fluorophores in addition to the grating, thedeformation will change the spacing between the diffraction lines or theangle between the beams diffracted from the grating.

A practical application of one or more of the disclosed embodiments isdepicted in FIG. 7. As shown in FIG. 7, the periodically structuredsurface 720, or grating, is defined on the surface of a structuralmaterial 710, which is shaped to define an engineering structure such asa pipe 700. FIG. 7 further illustrates that the structural material 710includes one or more fluorescent rods 730 embedded therein. Unlike thepreviously described exemplary embodiments, in this particular case, thesurface 720 is curved instead of flat. However, the principles heregenerally remain the same as those described in relation to the previousexemplary embodiments. In use, perturbations in the material 710 wouldresult in a modification of the diffraction pattern generated by thegrating 720 on the emission of the fluorescent rods 730.

It should be noted that the components of the exemplary configurationshown in FIG. 7 are represented in a relative scale that the depictedcomposite structure 700 not necessarily to scale or accurate topractical implementations. In particular, the grating 720 is representedby a mesh of lines; this mesh of lines is intended to represent gratingssimilar to those described in relation to FIGS. 1-6B, or any twodimensional gratings, with periodically defined groves, spacing, orholes. In addition the relative distance between the lines in such amesh is not representative of a practical distance between the grating'sfeatures with respect to the size of an object such as a pipe used, forexample, in a pipeline. As mentioned above, the size of the features inthe grating, or in the two dimensional photonic crystal arrangement, canbe defined in view of the size of the perturbation to be revealedthrough inspection. Similarly, as shown in FIG. 7, the fluorescentmaterial 730 is depicted as rods, however, it can be appreciated thatthe shape or arrangement of the fluorescent material within thecomposite structure does not necessarily have to be in rod form and theparticular shape, size and orientation can be adapted to the geometry ofthe system and to the type of spatial information that is revealed byinspection. In the specific case of parallel fluorescent rods, as shownin FIG. 7, the diffraction pattern generated by inspection of a sectionof the pipe in a direction around the central axis would be similar tothe one depicted in FIG. 6B.

As previously noted, the periodicity or dimensionality, of the gratingcan be larger than two (2). In the preceding exemplary configurations,only two-dimensional gratings were depicted: either two dimensionalgratings with one dimensional periodicity, such as the ones of FIGS. 1,2, 5A-5B, 6A-6B; or two dimensional gratings with two dimensionalperiodicity, such as the ones of FIGS. 3, 4, 7. Additional exemplaryconfigurations of composite structures that are constructed to includethree-dimensional gratings, with three-dimensional periodicity, alsoknown as three dimensional photonic crystals are further describedherein.

FIG. 8A-8B depicts an exemplary composite structure 800 constructed inaccordance with one or more of the disclosed embodiments to include arod like three dimensional photonic crystal as a grating, or diffractionelement. The photonic crystal represented in FIG. 8A-B is comprised ofrods of material 814, having a square cross section, distributed in sucha way that they form a three-dimensional periodic lattice. It can beappreciated that elongate “rods” having alternative three dimensionalshapes can be implemented as well. The structural material 810 can be asupport for the lattice with a different refractive index. However, insome implementations, the material can be absent if the lattice cansupport itself, and if the lattice is coupled to a structural materialin its proximity so as to detect the perturbation in the material in itsproximity.

The exemplary lattice can be functional by itself without the additionof a fluorophore, as it would be responsive to an inspecting radiationcreating regions of allowed bands and forbidden gaps according to acombination of Snell's law of refraction and Bragg's law of diffraction,as explained in the theory of photonic crystals and would be appreciatedby those in the art. By monitoring the energy and angular distributionof these band structures it is possible to quantify perturbations of thematerial, as such perturbations would change the periodicity of thelattice and thus the conditions for diffraction and refraction.

However, similarly to the previously described embodiments including twodimensional lattices, one or more fluorophores can be added within thestructure so as to facilitate more easy detection of the changes on thediffraction pattern caused by the three dimensional lattice on theemitting fluorophore or fluorophores. Such a fluorophore or fluorophorescan be added inside the volume 850 of the three dimensional lattice, asshown in FIG. 8A, or on the opposite side with respect to the observer.

If the fluorophore or fluorophores are added inside the photonic crystallattice, its distribution can be random given that, preferably, it isbelow at least 10 photonic crystal lattice planes counted from theobserver. FIG. 8B shows a section of the exemplary structure 800embodiment depicted in FIG. 8A with possible locations of thefluorescent elements indicated as black circles 860. The top side 865 ofthe structure shown in FIG. 8B is the one facing the observer. It can beappreciated that the scale in the figure is not accurate and therelative sizes of fluorophores and lattice elements are chosen only forthe sake of clarity. In practical implementations, the size of theindividual fluorescent elements can be orders of magnitude smaller thanthe lattice planes. Also the number of fluorescent elements is notnecessarily representative of a real case, as the fluorophore orfluorophores can be also uniformly distributed throughout a portion ofthe structure 800 below the grating or within the grating, occupying avolume approximately identified by the shaded area 870 in FIG. 8B.

As shown in FIG. 8B, the volume 870 that can be occupied by thefluorophore or fluorophores can also extend well below the photonicstructure, on the opposite side of the observer. As a result, the effectof the lattice on the emission radiation of the one or more fluorophoresis the formation of diffraction lines represented as dashed arrows inFIGS. 8A and B, e.g., 815. Such diffraction lines are similar to theones observed in X-ray diffraction for crystalline materials. In fact,from a physical point of view, the lattice 800 behaves like a crystal.The difference is the presence of one or more fluorophores, and that thesize of this lattice and the material properties that relate toinspection wavelength can be defined according to the application.Accordingly, as a function of the exemplary lattice structure andconstruction and by monitoring the position, presence, or absence ofthese diffraction lines, it is possible to measure information regardingthe perturbation affecting the material.

It can be appreciated that the particular geometry of the threedimensional lattice does not have to be necessarily the one shown inFIG. 8A-8B. For instance and without limitation, the lattice can beconstituted by a three dimensional periodic distribution of beads, asdepicted in FIG. 9, or of a material including a three dimensionaldistribution of holes therein, as represented in FIG. 10.

The photonic crystal 900 depicted in FIG. 9 has similar functionalitiesas the exemplary photonic crystal 800 shown in FIG. 8A-8B, however, thelattice is defined by a periodic distribution of beads 916 within asupporting material 910. The supporting material 910 can support thelattice and can have a different refractive index. In this exemplaryembodiment, a one or more fluorophores can be contained within thevolume 950 of the periodic lattice disposed within the supportingmaterial 910. Regarding the location and distribution of the fluorophoreor fluorophores similar considerations as for the embodiment of FIGS. 8Aand 8B are valid also for the configurations depicted in FIGS. 9 and 10.One difference of this exemplary configuration is that the beads 916themselves could be configured as fluorophores. For instance, the beadscan be luminescent nano-particles, quantum-dots, or micro-particlesactivated with a fluorophore added as a dopant. In addition oralternatively, the fluorophore can be a filler in between the gapsformed by the lattice of beads 916. The inspection and analysis can bedone in the same way as described for the embodiment depicted in FIG.8A-8B. As a result of the exemplary lattice structure, the effect of thelattice on the emission radiation of the fluorophore or fluorophores isthe formation of diffraction lines or directional forbidden gaps (orstop bands) represented as dashed arrows in FIG. 9, e.g., 915.

FIG. 10 depicts another exemplary configuration of a photonic crystal1000. As shown, the crystal 1000 includes a three dimensional latticethat is formed by a periodic distribution of holes 1016 formed within asupporting material 1010. Such holes, however, in some implementationsdo not necessarily have to be holes, and they can be regions of amaterial with a different refractive index than material 1010. Material1010 in this case is necessary as a support.

In FIG. 10 the volume/region within the material 1010 that includes thefluorophore or fluorophores is identified by the dotted volume 1050. Thevicinity of the dotted volume to the surface of the material withrespect to the number of photonic lattice planes identified by theperiodic elements is not to scale and representative of a real device.The functionality of this particular configuration is also similar tothe embodiments described in relation to FIGS. 8A-8B and 9. Bymonitoring the position of the diffraction lines 1015 it is possible togain information about the perturbations affecting the lattice, whichis, in turn, a function of the perturbations affecting the constituentmaterials.

The types of perturbations that are detectable as a function of theexemplary photonic crystals that are constructed in accordance with oneor more of the disclosed embodiments, are not limited to physicaldeformation and can also include temperature changes and changes in thechemical composition, liquid absorption, or functionalization of thecomposite structures. While these changes might not modify the spacingbetween the periodic features of the grating, they can cause a change inrefractive index. In turn such a change will modify the diffractionpattern by modifying the angle of refraction and, thus, the directionsof diffraction. In the exemplary configurations that do not include afluorophore, such material changes can cause a change of wavelength fora specific angle of observation. In the exemplary configurations thatinclude one or more fluorophores, the material changes can cause achange in the angle between the diffraction directions and thus a changein the spacing between the diffraction lines.

The distinction between a physical change and a change in temperature orin chemical composition is strait forward, because a physical change isgenerally localized on a small portion of the object, while the rest aredelocalized over larger areas. Nevertheless, there could be instances inwhich different types of perturbations affect the same areas; in thiscase it the different types of perturbations can be distinguished bycomparatively analyzing a reference material without a grating to detectany change in refractive index associated with changes in chemicalcomposition or temperature.

Once this correspondence between deformation and optical signal has beenestablished, the detection system can be used to quantify one in termsof the other. More specifically, as explained above the detection devicecan be used to reveal and quantify the perturbation in terms of theoptical signal. Conversely, it can be used to reveal and quantify thechange in wavelength or in diffraction angle as a material deformation.

Under the same principles of operation disclosed herein for constructingcomposite materials and detecting perturbations in materials, in someexemplary embodiments, an inspection device can be inversely calibratedto control and select a known band of wavelengths. More specifically thecontrol and selection of a known band of wavelength can be performed asa function of pressure that is applied on a material, or of anydeformation to which the material is subject. This application canprovide the optical dispersive element required in a monochromator orspectrometer wherein the principle of operation is based on a linearstress either in compression or in extension and does not require arotation. Usually, a monochromator is constituted of a grating coupledwith a slit: the grating divides the radiation, into its differentwavelengths at different angles. The slit positioned at a certaindistance from the grating only lets one wavelength through. In order tochange the wavelength that passes through the slit the grating isrotated so that a different diffraction angle is directed toward theslit. By applying a photonic structure as here described or a grating toa stretchable polymer or material, the wavelength selection can beperformed by varying the spacing of the periodic structure rather thanthe angle of observation. Accordingly, in this configuration it is notnecessary to rotate the grating to change the wavelength. An exemplaryconfiguration of the photonic structure used in a monochromator toprovide this complementary application of the technology is depicted inFIGS. 11A and 11B. FIG. 11A depicts an exemplary photonic structure 1100constructed in accordance with the disclosed embodiments in thesituation where the incident white light 1110 (or more in general aradiation containing multiple wavelengths) is reflected and diffractedby the photonic structure 1100 having a grating surface 1105 that, inthis example, is not deformed. The different wavelengths 1120 emergethus at different angles, and only a limited portion of them are able topass through the monochromator slit 1130. FIG. 11B represents thestructure 1100 (shown as 1100B) in the situation in which the photonicelement or the grating 1130B is stretched (e.g., from stress applied tothe structure), and, as such, the spacing of the periodic features ofthe grating is increased and thus the diffraction pattern 1120B changes.As a result the wavelength that emerges from the slit 1130B will bedifferent from the previous one (e.g., the relaxed photonic structure).In this way it is possible to achieve the same wavelength selectionperformed by a monochromator, but with a linear system based oncompression or extension of the photonic structure used in themonochromator. Therefore, if, for example, the grating material used inthe monochromator is a soft polymer such as PDMS, the wavelengthselection can be performed by applying pressure on it or a tensileforce.

The possible methods of fabrication utilized for the above mentionedembodiments can be many. Depositions of materials constituting differentlayers depicted in FIGS. 1 to 6 can be performed by spin coating, dropcasting, Sputtering, Physical Vapor Deposition, Chemical VaporDeposition, Molecular beam epitaxy, and the like. The structuring of thecomposite structure to obtain a 2 dimensional photonic crystal eitherwith 1D or 2D periodicity, can be also achieved in many different waysdepending on the application and on the size of the periodicity desired.One possibility is to use laser interference lithography, to impress apattern on a photoresist layer and successively etch it on thesubstrate. Another possibility is to use a mask to generate the desiredpattern also on a photoresist layer. Both these systems provide theability to achieve a size of the periodicity of below the micrometer.For smaller scales, the structuring can be done by electron beamlithography or stencil lithography. Another common way to fabricate adiffraction grating is by ruling the pattern using a ruling engine. Forlarger scale applications, it is possible to use molding techniques,such as injection molding, hot embossing, and the like.

Furthermore, when the photonic material only works in reflection and notransmission is required, the interface between the two materials withdifferent refractive index can be enhanced with the deposition of areflective layer, such as Aluminum, Copper, Chromium, Gold, and thelike.

The fluorophore or fluorophores can also be introduced into thecomposite structure in many different ways: for example a fluorophorethat is soluble in the polymer can be simply mixed into the polymerbefore curing: either in the elastomer or in the curing agent. Forinstance the fluorophore fluorescein can be dissolved in a variety ofepoxy polymers by dissolving it into the elastomeric portion beforecuring, and then curing it at room temperature. Another example could bethe utilization of metal nanoparticles such as Silver or Gold asfluorophores. These can be stabilized with the opportune ligand such asbenzoate and then dispersed into the curing agent of aPolydimethylsiloxane (PDMS) such as the curing agent of the Sylgard 184polymer kit of Dow Corning.

In case sharper emission transitions are required, then lanthanide ionscan be introduced as dopants in a polymer, a glass, or in a crystallinelattice. In case they need to be introduced into a polymer, they can bestabilized in it as complex as a coordination compound, while, if theyneed to be introduced into a glass or crystal, they can be added inionic form during growth: for example, the oxides of the lanthanides canbe added to the mixture of oxides forming the crystal before the startof a crystal growth technique, such as for example the flux growth.Other possible techniques to grow doped crystals include Czochralski,Hydrothermal growth, and the like.

In the case the fluorescent layer is not continuous like in FIGS. 1, 2,3 and 4, but it presents a discreet structure, such a structureddeposition can be achieved with one of the lithographic techniquesdescribed above for the fabrication of the photonic structure. Forexample, after a substrate has been etched through a photoresist afluorophore can be added to the substrate, before the removal of thephotoresist.

The embodiments represented in FIG. 8A can also be fabricated in asimilar manner alternatively etching and filling perpendicularlyoriented features on a substrate.

If these composite structures are sized above the micro scale, in casethe system is designed to interact with long wavelength radiations, suchas micro- or radio-waves, the fabrication methods are generally simplerthan below the micro scale and can be achieved with conventionalmolding, or rapid prototyping processes.

For the fabrication of a three dimensional photonic structure such asthe one depicted in FIG. 9 there is also a variety of techniques thatcan be utilized. For the nano and micro scale, a simple technique isself-assembly. For example Silica, Polystyrene, or Poly(methylmethacrylate) (PMMA) beads can self-organize themselves in a vertical orhorizontal deposition technique from the slow evaporation of adispersion of the beads. An alternative way is to form photonic crystalby shear-based nano-assembly of beads in polymers.

Inspection Device

In accordance with one or more of the disclosed embodiments, variousexemplary systems and methods for non-destructive inspection ofstructures to detect and quantify perturbations are further describedherein.

In some implementations, the inspection device can be used to analyzethe response of a photonic material to perturbations such as tensilestress, compressive stress, bending, deformation, changes intemperature, in chemical composition, and in refractive index. Althoughthe exemplary inspection device can be used independent of the exemplarycomposite structures that were previously described in relation to FIGS.1-10, the exemplary systems and methods for non-destructive inspectionare further described herein in relation to the previously describedcomposite structures.

More specifically, the inspection device is configured to emit aninspecting radiation into the material being inspected. As noted above,the composite structures previously described consist of a photonicmaterial whose periodicity can be affected by perturbations in itssurrounding. Such periodicity change results in a change in thediffraction pattern or photonic band structure generated by such aperiodic lattice. It can be appreciated that the lattice can be mono-,two-, or three-dimensional. The inspection device is further configuredto measure characteristics of the resulting diffraction pattern and,accordingly, measure the change in the diffraction pattern relative toan expected pattern.

Moreover the inspection device is configured to use, as an input, thechange in the diffraction pattern and provide, as an output, aquantification of the perturbation affecting the material. Inparticular, the inspection device is configured to transform thewavelength and the angle information about the diffracted radiation intoa measure of displacement. The inspection device consists of one or twocomponents together utilizing two similar principles to achieve such atransformation. One component transforms the wavelength information intoa displacement, while the other component transforms the angularinformation into a displacement. The periodic structure being inspectedconsidered could be for example the composite structure including adiffraction grating such as the one described in relation to FIG. 2.

According to a salient aspect, the inspection device is configured toquantify deformations in photonic materials through a wavelength change,or a diffraction angle change quantified from an intensity variation. Asa result, the inspection device provides the ability to detectperturbations with a sensitivity that is tunable through the choice ofthe inspecting wavelength and the corresponding periodicity of thephotonic material. Moreover, the inspection device provides amulti-dimensional level of sensitivity.

The system comprising the photonic material and the inspection device istunable to the size of deformation or defect that needs to be detected.For example, if the user is interested in detecting defects on the orderof few hundreds of nanometers, the distance between the periodicfeatures in the photonic structure needs to be at least on sub-micronscale. If the spacing is well above the micro scale, deformations on theorder of 100 nm might go unnoticed. While if the spacing is on the orderof tens of nanometers, the sensitivity will be for defects of similarscale and thus suitable to detect the defects of interest but notrequired, because over sensitive.

At the same time the inspecting radiation utilized in the inspectiondevice and the range of sensitivity of the device needs to be able tointeract with the features of the material. Therefore, for a sensitivityon the nanometer scale the radiation of the device needs to include thevisible range of the electromagnetic spectrum, and the sensor needs tobe sensitive to the same range. For the detection of larger scaledefects, for example millimeters, the spacing of the periodic featuresin the materials can be on the millimeter to the submillimeter range andthus it is sufficient for the inspecting radiation of the device toinclude infrared to microwave wavelengths.

The multidimensionality of the sensitivity is determined also by theconfiguration of the photonic material and the inspecting device. Forexample, for embodiments of the photonic materials with two dimensionalperiodicity such as the ones depicted in FIGS. 4, 6, and 7 ananisotropic deformation of the material that is larger along one axis(for example in FIG. 4 the axis perpendicular to the plane of the page)than along the other axis (in FIG. 4 the axis on the plane of the page)will result in the diffraction angles caused by the features along thefirst axis to be larger than the ones caused by the feature along thelatter axis. Therefore the spots 465 on the top surface of FIG. 4 thatare aligned perpendicular to the plane of the page will be farther fromeach other than the ones aligned along directions parallel to the planeof the page.

This two dimensional sensitivity that can be observed by naked eye fromthe embodiment in FIG. 4 can be also quantified by the inspectiondevice. For example this change in the spacing between the diffractionlines can be observed in an image captured by the camera sensor in thedevice 1260, or as a directional intensity change measured by the CCDarray 1214.

Turning briefly to the exemplary composite structure depicted in FIG. 2,the grating 220 is responsible for the diffraction, while the layer 250is fluorescent. While one or more fluorophores can be incorporated toenhance the detection of perturbations, it is not essential to theoperation of the exemplary inspection device. In fact, a gratingresponds to a white light source, by decomposing it into all differentwavelengths; while it responds to a laser beam by diffracting it intoseparate beams emerging from the grating at different angles dependingon the diffraction order, which is indicated in figure as m.Accordingly, the inspection device can be configured to emit one or moreelectromagnetic radiation sources including a diffused radiation source(such as a white light source) and a laser so as to be useable with avariety of different composite structure configurations (e.g.,irrespective of whether the structure includes a fluorophore).

Once the material is exposed to a white light source, such as the onecoming from an LED lamp, a diffraction pattern will be generated withdifferent wavelengths or colors being reflected and diffracted atdifferent angles. Each one of these wavelength for a specific angle ofobservation is related to the spacing between the periodic features ofthe grating according to the Grating Equation:nλ=d(sin β−sin α)  (1)

In case of a reflection grating or;nλ=d(sin β+sin α)  (2)

In case of a transmission grating, if for example the radiationdiffracted comes from a fluorescent layer located on the opposite sideof the gating with respect to the observer (as represented in FIG. 2),or if the inspection radiation simply hits the grating on the oppositeside with respect to the observer.

In equations (1) and (2) n is an integer number indicating the integernumber of wavelengths, λ is the wavelength, d is the spacing between twoadjacent periodic features, a is the angle of incidence, β is the angleof reflection, which coincides with the diffraction angle, when theseequations are satisfied.

In normal conditions, if the sample is not deformed by a defect, theperiodicity of the grating will be the same over the entire area, and itwill thus generate a smooth diffraction pattern, in which, at anyposition, the wavelength is changing smoothly with the angle ofobservation; or, for a single point of observation, the angle ischanging smoothly over the illuminated area, because different positionsstill correspond to different values of α and β. In the case of adefect, on the other hand, the change in wavelength (or color) inproximity and in correspondence to the defect will present anirregularity, as the periodicity of the grating will be locallymodified. By knowing the angles of diffraction, which are related to thearchitecture of the device (described hereafter) and by measuring thewavelength, observed, by using equations (1) and (2) the inspectiondevice can calculate the distance d between the periodic features andcompare it to the unperturbed d (spacing), which is pre-defined for thesample. The angles of incidence are known based on the relativepositions of the illuminating source and the observed spot on thematerial. The angles of diffractions are known by considering therelative position of the spot observed on the material and the sensor inthe device, or the size of the periodicity of the photonic structure onthe material. Alternatively, the same information can be derived fromthe distance between the radiation source and the sensor slit, and thedistance of the device from the photonic material. All these areparameters that can be initialized, modified, or fixed for the specificdevice, and/or a specific material.

Nevertheless, even if the architecture of the device (relative positionof radiation source and detector) and the size of the periodicity of thephotonic structure is not considered or known. The observation of thewavelength or diffraction angle change, with or without device, willstill allow a quantification of the perturbation or defect. The reasonis that the information required is not necessarily the absolute valueof displacement, but its relative change. Therefore, if throughout theanalyzed area of material the displacement appears as a certain valueand in a specific area appears as a different value, the more relevantinformation is the difference between these two values, rather that theabsolute values. For these reasons, in certain cases it might not benecessary to consider all of the parameters mentioned above, but justthe relative change. Conversely, if the knowledge of the exact value ofdisplacement is required, all configuration parameters can beconsidered, or the value displaced can be calibrated with the known sizeof periodicity (if even the starting value of periodicity is not known,it can be measured with microscopic techniques).

Furthermore, if none of the above parameters are known or also theinitial variation is too large and disordered (for example on a surfacethat is not smooth from the start) the quantification can be confirmedby comparing the diffraction pattern or the wavelength image (colorimage or photo-graph) with a reference image taken when the structure isapplied or at a significant point in time.

If, instead of diffused radiation, the material is exposed to a laserbeam, the laser beam will also be diffracted according to equations (1)and (2). The difference in this case is that the wavelength is constantand the diffraction conditions will be satisfied only at certain angles,resulting in an odd and symmetric distribution of diffracted beams. Ifthe material is not perturbed, the angular difference between thesediffracted beams will be the same throughout the material. However, ifthere is a deformation of the material, and thus of the periodicity ofthe grating, the diffraction angle between the beams will change. Bymonitoring this angle across the material it is possible to identifydeformed regions, by calculating d from equations (1) and (2), knowingthe λ, and measuring the angle.

In view of the above considerations, a configuration of the basiccomponents of an exemplary inspection device 1200 is further describedherein in relation to FIGS. 12A-12C.

In the exemplary embodiment shown in FIG. 12A, the inspection device1200 includes a laser 1220 and a diffused radiation source 1250, such asan LED white light source. Although source 1250 is described as adiffused electromagnetic radiation source, the source can also beconfigured to emit radiation with constant intensity over a certainrange of wavelengths, this range could be broad, or it could be limitedto a narrow range of wavelengths, it could be in the visible range or inany other range of the electromagnetic spectrum. Also shown is a lens1280, for focusing the radiation emitted by the diffused radiationsource 1250 and diffracted by a sample being inspected. The lens isconfigured to focus the diffracted radiation into a camera sensor 1260,which collects it and is further configured to provide the capturedimage to the processor 1216.

The inspection device can be arranged with various computer hardware andsoftware components that serve to enable operation of the inspectiondevice and, more specifically, perform operations relating to theanalysis of the information captured by the detector 1214. FIG. 12C is ablock diagram depicting these exemplary computer hardware and softwarecomponents of the inspection device 1200 including, the processor 1216and the circuit board 1215. As shown in FIG. 12C, the circuit board canalso include a memory 1230, a communication interface 1255 and acomputer readable storage medium 1235 that are accessible by theprocessor 1216. The circuit board and/or processor can also be coupledto the display 1217, for visually outputting information to the user,and a user interface 1225 for receiving user inputs and an audio output1270 for providing audio feedback to a user as would be understood bythose in the art: for example the device could emit a sound or a visualsignal from the display or from a separate indicator light when a defector deformation above a certain threshold is encountered. The thresholdcan be set manually or by default prior to the measurement through theuser interface which could be a touch screen or opportune keyboard.Although the various components are depicted either independent from, orpart of the circuit board 1215, it can be appreciated that thecomponents can be arranged in various configurations.

The processor 1216 serves to execute software instructions that can beloaded into the memory. The processor can be a number of processors, amulti-processor core, or some other type of processor, depending on theparticular implementation.

The memory 1230 and/or the storage 1235 are accessible by the processor1216, thereby enabling the processor to receive and execute instructionsstored on the memory and/or on the storage. The memory can be, forexample, a random access memory (RAM) or any other suitable volatile ornon-volatile computer readable storage medium. In addition, the memorycan be fixed or removable. The storage can also take various forms,depending on the particular implementation. For example, the storage cancontain one or more components or devices such as a hard drive, a flashmemory, a rewritable optical disk, a rewritable magnetic tape, or somecombination of the above. The storage also can be fixed or removable orremote such as cloud based data storage systems.

One or more software modules 1245 are encoded in the storage 1235 and/orin the memory 1230. The software modules can comprise one or moresoftware programs or applications having computer program code or a setof instructions executed in the processor 1216. Such computer programcode or instructions for carrying out operations and implementingaspects of the systems and methods disclosed herein can be written inany combination of one or more programming languages. The program codecan execute entirely on HMI 105, as a standalone software package,partly on the HMI and partly on a remote computer/device (e.g., controlcomputer 110) or entirely on such remote computers/devices. In thelatter scenario, the remote computer systems can be connected toinspection device through any type of network, including a local areanetwork (LAN) or a wide area network (WAN), or the connection can bemade through an external computer (for example, through the Internetusing an Internet Service Provider).

Included among the software modules 1245 is one or more analysisprograms that can be executed by the processor 1216. During execution ofthe software modules, the processor is configured to perform variousoperations relating to the analysis of the radiation captured by thedetector 1214 for detecting and quantify perturbations in the inspectedmaterials as a function of the diffraction pattern, as will be describedin greater detail below. It can also be said that the program code ofthe software modules 1245 and one or more of the non-transitory computerreadable storage devices (such as the memory 1230 and/or the storage1235) form a computer program product that can be manufactured and/ordistributed in accordance with the present disclosure, as is known tothose of ordinary skill in the art.

In addition, it should be noted that other information and/or datarelevant to the operation of the present systems and methods can also bestored on the storage 1235. For instance, the database 1285 can includeprescribed settings and parameters that relate to the various materialsand structures that can be inspected using the inspection device such asexpected diffraction patterns, characteristics of the materials anyperiodic gratings (e.g., orientation, period, spacing of features,optical parameters, transmission wavelength, etc.) or characteristics ofany fluorophore present in the material (e.g., excitation wavelength andemitted radiation wavelength) and the like, as will be discussed ingreater detail below. Similarly, the database can store otheroperational parameters that are specific to the inspection device andvarious modes of operation (e.g., diffused radiation based inspectionand laser-based inspection). It should be noted that although storage1285 is depicted as being configured locally to the storage of theinspection device, in certain implementations, database and/or variousof the data elements stored therein can be located remotely (such as ona remote computer or networked server—not shown) and connected to theinspection device through a network in a manner known to those ofordinary skill in the art. It can also be appreciated that the board1215 can also include or be coupled to a power source (not shown) sourcefor powering the inspection device.

A communication interface 1255 can also be operatively connected to theprocessor 1216 and can be any interface that enables communicationbetween the inspection device and external devices, machines and/orelements such as a control computer or a networked server (not shown).The communication interface includes, but is not limited to, a modem, aNetwork Interface Card (NIC), an integrated network interface, a radiofrequency transmitter/receiver (e.g., Bluetooth, cellular, NFC), asatellite communication transmitter/receiver, an infrared port, a USBconnection, and/or any other such interfaces for connecting theinspection device to other computing devices and/or communicationnetworks, such as private networks and the Internet. Such connectionscan include a wired connection or a wireless connection (e.g., using theIEEE 802.11 standard) though it should be understood that communicationinterface can be practically any interface that enables communicationto/from the inspection device.

Returning to FIG. 12A, in some implementations, the inspection device1200 can be configured to use the diffused radiation source 1250 toperform a preliminary analysis of the sample to identify an area of thesample presenting a deformation. Moreover, the inspection device can befurther configured to use the laser source 1220 to perform a moredetailed analysis of the identified area and to obtain a quantitativemeasurement of the deformation. However, it can be appreciated that theinspection device could consist only of one of these two radiationsources and provide reliable results. For instance, the wavelengthanalysis performed using the diffused radiation source could alsoprovide quantitative information as to the extent of the perturbation,as described above.

In particular, the diffused radiation source 1250 is configured to emita cone of radiation 1240 (delimited by the dotted lines in FIG. 12A).The photonic material, in response to this radiation (such as whitelight for example), will generate a pattern of diffraction by reflectingand diffracting different wavelengths along different directions. Thisdiffraction pattern will be focused through the lens 1280 into thecamera sensor 1260, which collects it and provides the captured image tothe processor 1216 for further analysis.

In case of a local perturbation the angular variation of wavelength willnot change as uniformly as in absence of perturbation. This abruptchange in color can be recognized by the processor 1216, which isconfigured by executing one or more of the software modules includingthe analysis software program. The processor can be further configuredto generate a notification accordingly. For instance, based on thegradient of the color change in the captured image, the processor cantransmit an alert signal such as a sound through an audio or lightemitter 1270. The processor can be further configured by executing theanalysis software to analyze the abrupt color variation identified bythe system. Moreover, the processor can be configured to associate aperiodicity size to the specific wavelength measured (as describedabove), and obtain the size of the perturbation by comparing it to areference such as the regular size of the periodicity measured in theunperturbed areas.

FIG. 13A illustrates an exemplary routine 1300 for analyzing the colorvariation to determine a periodicity size for the specific wavelengthmeasured with continued reference to the inspection device 1200 of FIGS.12A-12C. In particular, at step 1305, the processor 1216, which isconfigured by executing one or more of the software modules 1245including, the analysis software program, transforms the wavelength ateach specific point on the captured image to a size of the periodicityof the photonic material. As explained above, the transformation can beperformed as a function of the geometry of the device and the specificdiffraction angle corresponding to the specific wavelength spotanalyzed. Once the size of the periodicity has been determined, theconfigured processor can, at step 1310, compute the amount ofdeformation, by comparing it to the known periodicity in normalconditions. In addition or alternatively the periodicity can be comparedrelative to the determined periodicity of the surroundings, forinstance, to identify any differential that exceeds a prescribedthreshold. Then at step 1315, the configured processor can, using thecalculated deformation value, output the results on a display 1217 thatis coupled to the processor. Furthermore, at step 1315, the completeimage, or wavelength map can be output by the configured processor usingthe display 1217. In addition, the information can be stored by theprocessor in the storage 1235 and/or sent via the communicationsinterface 1255 to a computing device or over a network to a centralizedprocessing center server (not shown) for further analysis and/orstorage. FIG. 11 depicts two side-by-side visual images of thewavelength map generated and output by the inspection device for asample being inspected. In particular, on the left side of the image,the map is shown without stress applied to the sample and, on the rightside of the image, the map of the sample is shown while stress isapplied to the sample.

An alternative method for detecting and analyzing perturbations of thesample material is based on the diffraction of the laser beam 1230. Asshown in FIG. 12A, the incoming beam 1290 is the diffracted beamresulting from the interaction of the emitted laser beam 1230 with thephotonic sample material. This beam 1290 can be detected by a detector1214, and its position on the detector will be indicative of thediffraction angle, which is related to the size of the periodicity ofthe photonic material according to equation (1) above. In FIG. 12 thereare two extra elements depicted including a mirror 1212 and a lens or anoptical filter 1213 to modulate the intensity of the beam. Both theseelements are not required for the basic functioning of the inspectiondevice 1200, however, they can be beneficial in that they can provide amore efficient measurement. In particular, the presence of the mirror1212 can extend the optical path and direct the beam to the location ofthe detector, which can be defined with the goal of minimizing the sizeof the device, for example. Moreover, the inspection device 1200 can beconfigured to include more than one mirror for this purpose.

The function of element 1213 could be one or more of, a filter to reducethe intensity of the laser in order not to saturate the detector or aconcave lens to diffuse the beam. Such an arrangement can be used todecrease the intensity of the beam 1290 and distribute it over a largerarea of detection on the detector 1214. For instance, to enable multiplesimultaneous measurements from different sensor units that define thedetector 1214. In some implementations, the detector (or detectors) 1214can be a photodiode positioned on the path of the beam when the materialis in normal conditions, or it could be a CCD array with differentsensitive elements, so that any change in the diffraction angle willresult in the beam hitting the detector in different positions. Thephotodiode or CCD array can be configured to transform the intensity ofradiation into intensity of electric current. Moreover, this current canbe converted to a voltage, which can then be used as input for theprocessor. Accordingly the processor can be configured to convert thevoltage input into a measure of deformation of the inspected sample.

More specifically, FIG. 13B illustrates an exemplary routine 1350performed by the processor for quantifying the deformation of thematerial. In particular, at step 1355, the processor, which isconfigured by executing one or more of the software modules 1245,including the analysis software, converts the received voltage into aposition of the beam on the detector. For instance, this conversion canbe performed as a function of the known location of the sensing elementsthat comprise the detector 1214. Then, as explained above, at step 1360,the configured processor, based on the geometry of the device, canconvert the calculated position to an angle of diffraction. Then at step1365, the processor converts the angle of diffraction into a periodicityof the photonic material. At step 1370, the processor compares thisdetermined periodicity to the know periodicity in case of nodeformation, and, at step 1375, outputs and stores a quantified valuefor any deformation.

Turning briefly to FIG. 16A-16B, which depict exemplary images (e.g.,wavelength maps) of light captured by an exemplary inspection devicefrom inspection of a composite structure constructed in accordance withthe disclosed embodiments. FIGS. 16A and 16B are further examples of howan exemplary structural material constructed in accordance with thedisclosed embodiments would diffract light, in absence and in presenceof a force applied to it. As shown in the FIGS. 16A-16B, the color/shadeor diffracted wavelength at each specific point on the material canchange depending on the force applied to the material and itsdeformation. More specifically, FIG. 16A, represents imagery of aninspected material in the situation where the incident white light (ormore in general a radiation containing multiple wavelengths) has beenreflected and diffracted by the photonic structure described herein as agrating that, in this example, is not under stress. FIG. 16B representsthe situation in which the same photonic element or the grating isstretched (e.g., from stress), the spacing is increased and thus thediffraction pattern changes.

The visual map shown in FIG. 16A-16B constitutes an example of therefracted radiation information captured as an input for the inspectingdevice. After processing and transformation of wavelength todisplacement, the output of the inspection device can also berepresented as a color map in 2 dimensions if each color is defined tocorrespond to a certain value of displacement. It has to be noted,however, that the information related to the apparent color or shadingof the two exemplary images is provided as an example and can bedifferent. Therefore, input and output could look similar, whilecontaining different information.

In case the analysis is performed with a laser beam, rather than with adiffused radiation, the pattern won't be uniform, but it will consist ofregularly distributed spots such as the ones visualized in FIGS. 1 and 4(e.g., 160A, B, C, D, E, and 465). The 2D image captured as aconsequence of diffused irradiation simultaneously provides informationon a larger area of sample, as the illuminated area is larger.Conversely, the image of the diffraction pattern generated by thediffraction of the laser beam provides information relative to the areailluminated by the laser. This latter configuration, can be moresensitive and can be advantageous when small displacements are expectedto occur uniformly over a larger area of the sample. Alternatively, thediffused irradiation can be used as a preliminary analysis and the laserirradiation as a subsequent more detailed analysis.

FIG. 12B depicts the inspection device 1200 of FIG. 12A from a frontperspective view, so that it is possible to visualize the windows 1218arranged such that the radiation can exit and enter the inspectiondevice 1200. In particular, the window for the collection of thediffracted laser beam is identified as 1218A, the window for thecollection of the image as a wavelength map 1218B, the window for thediffused radiation to exit the device is identified as 1218C, and thewindow for the laser beam to exit the device is identified as 1218D.

An alternative, more compact arrangement of the components of theinspection device 1200 is depicted in FIGS. 14A and 14B. FIG. 14A is afront perspective view of this variation of the device 1200 in a morecompact configuration and FIG. 14B is a rear perspective view. Withrespect to the particular the elements incorporated into the exemplarycompact inspection device configuration and the principles of operation,this exemplary variation is substantially equivalent to the inspectiondevice 1200 depicted in FIGS. 12A and 12B. As such, the respectivecomponents are numbered consistently. However, in order to minimize thespace utilized, the two light sources are arranged one on top of eachother. In particular, the lamp 1250 is represented on top of the laseremitter 1220, however, it can be appreciated that the sources 1250 and1220 could also have the opposite arrangement. One advantage of havingthe laser on the bottom is that it is at the same level as the laserdetection system, thus it is easier to collect the beam and direct it tothe detector if it is on the same plane. Nevertheless, it can beappreciated that additional components for directing the beam to thedetection system can be easily incorporated into the inspection deviceif the light source is not exactly on the same plane as the detector. Inaddition, the exemplary configuration of the inspection device 1200shown in FIGS. 14A-14B is also depicted as having batteries 1219 as apower source.

Although the exemplary embodiments are depicted in FIGS. 12A-14B in ahigh-level (e.g., simplified) form, in accordance with one or moreembodiments, the inspection device, can be configured to have a morebasic configuration. As noted previously, the inspection device caninclude only one light source (e.g., 1220 or 1250) and the correspondingdetection components and does not necessarily require both types ofsources at the same time, as each one of the systems can independentlybe used to provide quantitative information regarding perturbations.Moreover one or more of the optical elements such as mirrors and lensescan removed without departing from the scope of the disclosedembodiments.

Nevertheless, there are other possible embodiments that are configuredto implement different systems and methods for detection, which can beadvantageous for certain practical applications. In particular, oneexemplary alternative option to collect the diffracted laser radiationand direct them to a detector that simply measures the intensity, is tocollect more than one diffracted beam and focus them on the detectorwith a lens, or a system of lenses. A high-level diagram of an exemplaryinspection device 1500 having such a configuration is shown in FIGS. 15Aand 15B. In particular, FIG. 15A is a top view and FIG. 15B is a frontperspective view of the inspection device 1500.

This particular configuration of the inspection device is generallyanalogous to the configuration described in relation to FIGS. 12A-14B.However, an additional feature is the presence of two lenses 1511 and1513 disposed on the path of two incoming laser beams 1590 and 1595. Inthis configuration, both beams are collected by lens 1511, which reducestheir divergence or, if possible, can also generate some level ofconvergence. Both beams are then reflected by the mirror 1512 throughanother lens 1513. The lens 1513 could be necessary, or not, dependingon the initial divergence of the beams and by the power of lens 1511.The purpose of additional lens 1513, if not already achieved throughlens 1511, is to focus the two beams on a sensitive part of aphoto-diode 1514, which transforms the intensity of the radiation into acurrent.

In case of deformation of the photonic material, the convergence of thebeam onto the photodiode should be compromised. In particular, if thedivergence of 1590 and 1595 changes, the focal point or intersectionpoint of the two beams will occur either before or after the photodiode.This will cause an intensity change in the current generated by thephotodiode 1514. Accordingly, through calibration, the processor 1516,which is coupled to the photodiode, can be configured to associate adeformation size on the sample material to a given intensity variationmeasured at the photodiode. A summary of the steps performed by theprocessor 1516, which is configured by executing an analysis softwareprogram, to transform intensity to deformation size can include:calculate the diffraction angle of the beams based on the focus of thetwo diffracted laser beams on the photodiode and a well-defineddivergence angle of the beams at the position of lens 1511. Usingequation (1) and the diffraction angle, the configured processor canthen calculate the periodicity spacing responsible for such a calculateddiffraction angle.

Therefore, a change in the periodicity of the grating caused by aperturbation will result in a change in intensity on the detector. Theintensity of electric current generated by the photodiode, which isproportional to the intensity of radiation, can be converted to avoltage and the voltage can be processed by the processor unit 1516 togenerate a value of deformation on the material by comparing it to theintensity collected in normal conditions. The calculations performed bythe processor are as described in the previous paragraph. Thisinformation from the processor can then be sent to a display 1517, whichshows the quantitative information relating to the perturbations.

In FIGS. 15A and 15B there are two lenses and one mirror, which, asexplained earlier are not always necessary for the operation of theinspection device 1500. Nevertheless, there could be also a highernumber of lenses and mirrors to achieve the same function and, in someinstances, in a more effective way. For example, if the divergence ofthe two laser beams is very high, more lenses can be required in orderto focus the beam on the detector 1514. For the same reason, moremirrors might be required simply to increase the optical path of thelaser beams inside the device in order to achieve the desiredconvergence. Alternatively, if, for the minimization of space and theoptimization of the position of the different elements inside thedevice, the detector might be in a hard to reach position or hiddenbehind another element. For this reason more mirrors might be requiredfor the beam or beams to reach the detector or the desired element.

In addition, alternative configurations of the exemplary inspectiondevice can provide more degrees of freedom and a higher level ofdimensionality in the measurement of perturbations that are performed.As the photonic materials, for instance the exemplary compositestructures previously described, can be configured to have varyingdimensionality (e.g., a one, two or three dimensional grating), theinspection device can also be configured to detect and present higherdimensionality. For example, if the photonic material consists of a twodimensional lattice, the inspection device can be configured to detectchanges in the angle of diffraction not only on one plane, but on twoplanes. In such a configuration, the diffracted laser (e.g., beam 1290of FIG. 12, for example) can move sideways with respect to the detector,and can also move vertically as a function of the perturbation. In thiscase the angular variations in the diffracted beam won't be onlyanalyzed on the plane of the device, but also in the plane perpendicularto it. Therefore the device will present mirrors, lenses, and detectorssetup to receive, work and analyze on beams that are alignedperpendicularly to the plane of FIGS. 13A and 16A. Accordingly, theinspection device can be configured so as to detect this two dimensionalmovement of the diffracted laser. More specifically, in someimplementations, the detector 1214 of the inspection device can becomprised of a planar group of CCD arrays, say, on top of each other, orin any other two dimensional sensing arrangement. The diagram of thesystem will generally be analogous to the one in FIG. 12 (and also theinspection device of FIG. 14A or 15A, for example), with the onlydifference that the sensitivity of the device will be enhanced due tothe variation in the particular design of the detector. As a result, theinspection device will not only be able to detect the presence of adeformation and quantify it, it will also be able to define theanisotropic shape or directionality of such a deformation, by measuringa displacement along two different directions according to the twodimensional configuration of the device and photonic structure explainedabove.

Moreover, in order for the inspection device to be used for a threedimensional photonic system such as a photonic crystal described inrelation to say, FIGS. 8A-10, the inspection device can be configured tocapture and analyze multiple diffraction lines at the same time throughdifferent windows and detect the diffraction angle variation. Therelative position of the windows with respect to the inspecting beam isdefined as a function of the specific structure of the three dimensionallattice or photonic crystal considered. For example, a three dimensionalphotonic structure with a photonic band gap will generate a diffractionpattern of allowed band and forbidden gaps along different directionsdetermined by the different lattice planes. Therefore, it will bepossible to monitor the absence or the decrease of radiation of acertain wavelength along a certain direction. For example, considering a3D opal with a face-centered cubic (fcc) lattice, this will give rise toa set of photonic stop bands or band gaps, if the quality of the latticeis very high. Few of these stop bands or band gaps are more intense thanothers and can be collected at angles that are not too different fromeach other. In particular the stop bands corresponding to the latticeplanes having Miller indices of, for instance, 111, 220, and 200, couldall be gathered (as explained above) and monitored by the device.Therefore, if there is an increase in intensity corresponding to aspecific stop band along a specific direction, this it will indicatethat the spacing between the corresponding lattice planes has changed.Furthermore, if the movement of the stop band can be monitored by a 2Ddetector such as two or more CCD arrays, this will also indicate if thelattice displacement is in compression or extension. According to thispossibility to monitor the movement (in angle and intensity) ofdifferent stop bands or band gaps independently, this analysis willprovide multidimensional information (as many dimensions as the numberof stop bands analyzed) about the anisotropy of the deformationoccurring inside the lattice along the different directions analyzed.

Although this method would work also without a fluorophore as explainedabove, the presence of a fluorophore would greatly simplify themeasurement. In presence of one or more fluorophores, the incidentradiation can target the optical excitation of the fluorophores, so thatthe analysis can be performed on their emission. In such a scenario, theemission of the fluorophore would be irradiated isotropically in alldirections independently on the direction of excitation. However, itsintensity would be drastically reduced by the presence of stop bands orband gaps along specific directions determined by the lattice constantsor the different planes and wavelength or emission of the one or morefluorophores. Therefore, by conforming the device in such a way that itmonitors the absence of intensity along any or all of those directions,it will be possible to determine the presence of displacement bymonitoring the intensity change. This would thus provide amultidimensional (as many dimensions as the stop bands analyzed) ananisotropic analysis of the deformation of the material and of anychange that determines a variation of the refractive index or emissiveproperties of one or more or the materials included in the system. Thesechanges could be, for example and without limitation, temperaturechanges, chemical absorption, functionalization, presence of magneticfields, exposure to other types of radiations.

Two other practical implementations of the disclosed embodiments of theinvention are represented in FIGS. 16 and 17. The main differencebetween these exemplary inspection devices and the previously describedinspection devices is the capability to move the light source. In FIG.16 the light source can be a diffuse radiation source 1701 or a laser1704, or both at the same time. Such source is attached to a movable arm1703 which can slide over another arm 1702, in order to adjust itsdistance from the body of the device, which in this figure isrepresented as cylindrical. Arm 1702 can rotate around the device and isheld in place by a railing system 1601 placed around the device. Theradiation emitted by the source 1704 is indicated as 1705, this isdiffracted from the material and sent into the device following apossible path traced by the dotted line 1705. Such a radiation willenter the device from a window 1706 and potentially be reflected by oneor more mirrors 1707 to reach the detector 1708. Even in this case thepresence of the mirrors is not required, but it could facilitate theoptimization of the architecture of the device. 1709 is the processorand 1710 a touch screen or a simple screen for the visualization of thedata and results. The advantage of having a camera moving with respectto the sensor is that it makes it easy to collect radiation fromdifferent directions and thus monitor different diffraction conditions(for 2 dimensional photonic materials) or different stop bands/band gaps(for 3 dimensional photonic materials). Even in this case, if the lightsource is diffused, the camera sensor that can be placed in proximity ofthe window 1706 will monitor changes in the wavelength diffracted ateach point, while if the source is a laser, the absence and presence ofradiation, or the intensity of radiation will provide informationregarding the displacement of the material.

In FIG. 17 the principle utilized is the same, the main difference isthat this embodiment focuses on the user interface. The entire systemcan be adapted and miniaturized on a device similar to a tablet hererepresented. The dashed line 1806 represents a touch screen on thedevice on the opposite side with respect to the current view. The backside of the device here appearing on the top of the figure includes thelight sources 1802 and 1808 on movable arms that can rotate in circlearound a certain spot. This spot doesn't necessarily have to be in thecenter of the device, but it can be located as it is more convenient.The light sources can also slide along the movable arms 1801 so thatthey can be placed anywhere on a circular area 1805 and thus coverseveral diffraction angles. The rotating arm can move around a circularsupport 1803. In case the radiation source is a laser 1802, one of thepossible paths of the beam is traced by a dashed line: it is reflectedand diffracted by the photonic material and redirected toward window1804 of the device which can be the sensitive element of the detectoritself, or a window that lets the beam through to the detector or to oneor more mirrors as shown in the previous embodiments. If the diffusedlight source is utilized, the image of the diffraction pattern will beanalyzed by a camera sensor 1804. It is to be noted that element 1804can be either the camera sensor, or photodetector, or both, or a windowthat lets the radiation through, so that it can reach the opportunesensitive element either directly or with a set of mirrors, or otheroptical elements.

At this juncture, it should be noted that although much of the foregoingdescription has been directed to systems and methods for providingcomposite structures, the systems and methods disclosed herein can besimilarly deployed and/or implemented in scenarios, situations, andsettings far beyond the referenced scenarios.

It should be appreciated that more or fewer operations can be performedthan shown in the figures and described. These operations can also beperformed in a different order than those described. It is to beunderstood that like numerals in the drawings represent like elementsthrough the several figures, and that not all components and/or stepsdescribed and illustrated with reference to the figures are required forall embodiments or arrangements.

Thus, illustrative embodiments and arrangements of the present systemsand methods provide a system and a computer implemented method, computersystem, and computer program product for wirelessly configuring fielddevices. The flowchart and block diagrams in the figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods and computer program products according to variousembodiments and arrangements. In this regard, each block in theflowchart or block diagrams can represent a module, segment, or portionof code, which comprises one or more executable instructions forimplementing the specified logical function(s). It should also be notedthat, in some alternative implementations, the functions noted in theblock may occur out of the order noted in the figures. For example, twoblocks shown in succession may, in fact, be executed substantiallyconcurrently, or the blocks may sometimes be executed in the reverseorder, depending upon the functionality involved. It will also be notedthat each block of the block diagrams and/or flowchart illustration, andcombinations of blocks in the block diagrams and/or flowchartillustration, can be implemented by special purpose hardware-basedsystems that perform the specified functions or acts, or combinations ofspecial purpose hardware and computer instructions.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the disclosure.As used herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising”, when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

Also, the phraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting. The use of“including,” “comprising,” or “having,” “containing,” “involving,” andvariations thereof herein, is meant to encompass the items listedthereafter and equivalents thereof as well as additional items.

The subject matter described above is provided by way of illustrationonly and should not be construed as limiting. Various modifications andchanges can be made to the subject matter described herein withoutfollowing the example embodiments and applications illustrated anddescribed, and without departing from the true spirit and scope of thepresent disclosure, which is set forth in the following claims.

What is claimed is:
 1. A composite photonic structure, comprising: oneor more layers of a structural material; a diffractive grating inregistry with the one or more layers of structural material, the gratingincluding a plurality of features that are arranged to have periodicityin at least one dimension; and a fluorophore material disposed withinthe composite structure.
 2. The structure of claim 1, wherein thegrating is one or more of: a discrete layer of one or more gratingmaterials disposed over an entire surface of the one or more layers ofstructural material, and defined by a surface of the one or more layersof structural material, and wherein the structural material is anon-metallic material.
 3. The structure of claim 2, wherein the gratingextends over one or more of a top surface and a bottom surface of atleast one of the one or more layers of structural material.
 4. Thestructure of claim 2, wherein the grating layer separates two layers ofstructural material.
 5. The structure of claim 1, wherein the pluralityof features of the grating are arranged to have periodicity in at leasttwo dimensions.
 6. The structure of claim 1, wherein the fluorophore isof the type that is excited by radiation having a first wavelength andemits radiation having a second wavelength upon excitation, and whereinthe one or more layers of structural material and the grating are atleast partially transparent to radiation having the first and secondwavelengths.
 7. The structure of claim 6, wherein the fluorophore isincorporated into the structure as one of: a separate layer of materialthat includes at least the fluorophore material, and a dopant ornano-material that is embedded in a region within at least one of theone or more layers of structural material.
 8. The structure of claim 7,wherein the fluorophore material is arranged within the compositestructure to have consistent periodicity in at least one dimension. 9.The structure of claim 7, wherein the fluorophore material extendsthroughout a cross-sectional area of the composite structure.
 10. Thestructure of claim 6, further comprising; a first set of elongate rodsincluding the fluorophore material embedded within the one or morestructural material layers, wherein the rods in the first set areoriented parallel to one another and are spaced apart to have consistentperiodicity in at least one dimension.
 11. The structure of claim 10,further comprising; a second set of elongate rods including thefluorophore material embedded within the one or more structural materiallayers, wherein the rods in the second set are oriented parallel to oneanother and are spaced apart to have consistent periodicity in at leastone dimension, and wherein the second set of rods are orientedperpendicular to the first set of rods.
 12. The structure of claim 6,wherein the grating is a layer of one or more grating materials andwherein the fluorophore material is provided within the grating layer.13. The structure of claim 6, wherein the fluorophore layer is arrangedbetween the one or more layers of structural material thereby separatingtwo layers of structural material.
 14. The structure of claim 6, whereinthe fluorophore material is fluorophore is embedded within thestructural material as one or more of: a dopant and a nano-material. 15.The structure of claim 1, wherein the grating features have periodicityas defined by a first value, and wherein the first value is defined asfunction of a size of perturbations to be detected during use of thecomposite structure.